Activation of Ras/Raf protects cells from melanoma differentiation-associated gene-5-induced apoptosis

Abstract

Melanoma differentiation-associated gene-5 (mda-5) was the first molecule identified in nature whose encoded protein embodied the unique structural combination of an N-terminal caspase recruitment domain and a C-terminal DExD/H RNA helicase domain. As suggested by its structure, cumulative evidences documented that ectopic expression of mda-5 leads to growth inhibition and/or apoptosis in various cell lines. However, the signaling pathways involved in mda-5-mediated killing have not been elucidated. In this study, we utilized either genetically modified cloned rat embryo fibroblast cells overexpressing different functionally and structurally distinct oncogenes or human pancreatic and colorectal carcinoma cells containing mutant active ras to resolve the role of the Ras/Raf signaling pathway in mda-5-mediated growth inhibition/apoptosis induction. Rodent and human tumor cells containing constitutively activated Raf/Raf/MEK/ERK pathways were resistant to mda-5-induced killing and this protection was antagonized by intervening in this signal transduction cascade either by directly inhibiting ras activity using an antisense strategy or by targeting ras-downstream factors, such as MEK1/2, with the pharmacological inhibitor PD98059. The present findings provide a further example of potential cross-talk between growth-inhibitory and growth-promoting pathways in which the ultimate balance of these factors defines cellular homeostasis, leading to survival or induction of programmed cell death.

Central role of interferon regulatory factor‐1 (IRF‐1) in controlling retinoic acid inducible gene‐I (RIG‐I) expression

“…Type I IFNs have profound growth-suppressing properties and the CARD domain present in these molecules supports their involvement in caspase recruitment and apoptosis. Indeed, we have demonstrated that overexpression of mda-5 alone induces apoptosis in a variety of cells (Kang et al, 2002;Lin et al, 2006a). These findings suggest that in addition to the anti-viral effects, RIG-I and mda-5 might also mediate the growth suppression properties of IFNs.…”

New and Old Genes Associated with Topotecan Resistance Development in Ovarian Cancer Cell Lines

“…It can also induce death of virus-infected cells by a mechanism involving DNA fragmentation (31). It has been reported that ectopic expression of IFIH1 gene can induce death of cancer cells (32). However, the role of IFIH1 in drug resistance has not been so far described.…”

MDA-5 Is Cleaved in Poliovirus-Infected Cells

“…Rabbit antibody against MDA-5 was produced by immunizing rabbits with a purified protein encompassing the first 335 amino acids of the protein linked to glutathione S-transferase (27). Mouse monoclonal anti-EF1␣ was purchased from Upstate USA Inc., Chicago, IL.…”